ES2601397T3 - Process for preparing bitumen compositions with reduced hydrogen sulfide emission - Google Patents

Abstract

The method for preparing a polymer modified asphalt having reduced hydrogen sulfide emissions, which comprises a. heating a mixture of asphalt and a conjugated diene vinyl / elastomeric aromatic polymer; b. add a crosslinker to the mixture where the crosslinker is elemental sulfur; and, c. add an H2S sweeper of inorganic or organic metal salt to the polymer modified asphalt in an amount ranging from 0.05 to 3% by weight based on the mixture of asphalt and polymer, where the H2S sweeper metal of salt Metallic is selected from the group consisting of zinc, cadmium, mercury, copper, silver, nickel, platinum, iron, magnesium and mixtures thereof.

Description

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DESCRIPTION

Process for preparing bitumen compositions with reduced emission of hydrogen sulfide Field of the invention

The present invention relates to hydrocarbon-based binders, such as bitumen, asphalts and tars that are particularly useful as industrial coatings and bitumen for the road or the like. It refers particularly to processes for obtaining bitumens or bitumens that have reduced the evolution of hydrogen sulfide.

Background of the invention

The use of bitumen (asphalt) compositions in the preparation of aggregate compositions (including, but not limited to, bitumen and rock) useful as road paving material is complicated by at least three factors, each of which which imposes a serious challenge to provide an acceptable product. First, bitumen compositions must meet certain performance criteria or specifications to be considered useful for road paving. For example, to ensure acceptable performance, state and federal agencies publish specifications for various applications of bitumen that include specifications for use as road pavement. Current Federal Highway Administration specifications require a bitumen (asphalt) product that meets defined parameters related to properties such as viscosity, firmness, penetration, hardness, toughness and ductility. Each of these parameters defines a critical feature of the composition of bitumen, and compositions that fail to satisfy one or more of these parameters will make that composition unacceptable for use as a road pavement material.

Conventional bitumen compositions often cannot meet all the needs of a particular specification simultaneously and, if these specifications are not met, damage to the resulting road may occur, which includes, but is not necessarily limited to, permanent deformation, rupture Thermally induced and flexural fatigue. This damage greatly reduces the effective life of paved roads.

In this regard, it has long been recognized that the properties of conventional bitumen compositions can be modified by the addition of other substances, such as polymers. A wide variety of polymers have been used as additives in bitumen compositions. For example, copolymers derived from styrene and conjugated dienes, such as butadiene or isoprene, are particularly useful, since these copolymers have good solubility in the bitumen compositions and the resulting modified bitumen compositions have good rheological properties.

It is also known that the stability of the polymer-bitumen compositions can be increased by the addition of crosslinking agents (vulcanizing agents) such as sulfur, often in the form of elemental sulfur. The addition of external sulfur is used to produce improved stability, even if the bitumen naturally contains varying amounts of natural sulfur.

Accordingly, a process for preparing a bitumen-polymer composition consisting of mixing a bitumen, at 130-230 ° C (266-446 ° F), with 2 to 20% by weight of a block or random copolymer is known , which has an average molecular weight between 30,000 and 500,000. The resulting mixture is stirred for at least two hours, and then 0.1 to 3% by weight of sulfur is added with respect to the bitumen and the mixture is stirred for at least 20 minutes. The amount of sulfur added can be 0.1 to 1.5% by weight with respect to bitumen. The resulting bitumen-polymer composition is used for road coating, industrial coating or other industrial applications.

Similarly, a polymer asphalt (bitumen) composition obtained by hot mixing asphalt with 0.1 to 1.5% by weight of elemental sulfur and 2 to 7% by weight of a natural or synthetic rubber is known, which can be a linear butadiene / styrene copolymer. A process for preparing a rubber modified bitumen by mixing rubber, either natural or synthetic, such as styrene / butadiene rubber, with bitumen at 145-185 ° C (293-365 ° F), in an amount up to 10% by weight based on bitumen, then adjusting the temperature to 125-204 ° C (257-400 ° F), and mixing in the mixture a minimum amount of sulfur so that the weight ratio of sulfur to rubber is between 0.01 to 0.9. A catalytic amount of a vulcanized accelerator is then added to effect vulcanization. A critical nature of the ratio of sulfur to rubber is sometimes presented, for example, that the weight ratios of sulfur to rubber of less than 0.01 give modified bitumen of inferior quality.

The second factor that complicates the use of bitumen compositions affects the viscosity stability of said compositions under storage conditions. In this regard, bitumen compositions are frequently stored for up to 7 days or more before being used and, in some cases, the viscosity of the composition may increase so much that the bitumen composition cannot be used for its intended purpose. On the other hand, a stable bitumen composition in storage provides only a few increases in viscosity and, consequently, after storage it can still be used for its intended purpose.

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Asphalt concrete, which typically includes asphalt and aggregate, asphalt compositions to re-coat the surface of asphalt concrete, and similar asphalt compositions, must show a certain number of specific mechanical properties to allow use in various fields of application, especially when asphalts are used as binders for surface coatings (road coating), as asphalt emulsions, or in industrial applications. (The term "asphalt" is used herein interchangeably with "bitumen." Asphalt concrete is asphalt used as a binder with appropriate aggregate added, typically for use on roads.) The use of asphalt or asphalt emulsion binders either in maintenance coatings as a surface cover or as a very fine bituminous mixture, or as a thicker structural layer of bituminous mixture in asphalt concrete, is improved if these binders have the requisite properties such as desirable levels of elasticity and plasticity.

An additional concern in the production of road grade asphalt (road grade asphalt is any asphalt intended to pave the east or unmodified road with polymer), roofing asphalt and other bitumen is that occasionally undesirable levels of sulfur are generated of hydrogen (H2S) during the production, storage and application of asphalt. It is desirable if the H2S level could be reduced or eliminated in these cases. Hydrogen sulfide is a colorless, toxic gas with an offensive stench and is said to smell like rotten eggs. H2S is dangerous for workers and also causes pyrophoric iron pyrite formation in storage tanks.

As can be seen from the above, methods for improving road asphalt are known. The elements necessary for the commercial success of any of these procedures include keeping the procedure as simple as possible, reducing the cost of the ingredients, and using available cuts of asphalt from a refinery without mixing in more valuable fractions. In addition, the resulting asphalt composition must satisfy the physical physical properties mentioned above and environmental problems, such as the reduction of H2S. Thus, it is an industry goal to reduce the release of hydrogen sulfide from asphalt without sacrificing any of the other elements and improving asphalt properties as much as possible.

Compendium of the invention

A method is provided to reduce hydrogen sulfide emissions from polymer asphalt compositions, which involves adding a sweeping of H2S of inorganic or organic metal salt, to the asphalt in an amount effective to reduce the evolution of H2S. The metal of the H2S sweeper of inorganic or organic metal salt may be zinc, cadmium, mercury, copper, silver, nickel, platinum, iron and / or magnesium, mixtures thereof of these salts.

A polymer asphalt composition is also provided that includes a sweeper of H2S of inorganic or organic metal salt in an amount effective to reduce the evolution of H2S. Again, the sweeper metal of H2S of inorganic or organic metal salt can be zinc, cadmium, mercury, copper, silver, nickel, platinum, iron, and / or magnesium, and mixtures of these salts. The description also includes road and roof coverings made of these asphalts and methods for this.

In another non-limiting embodiment of the description, an asphalt composition is provided, which includes a polymer asphalt composition that includes asphalt, aggregate, and an H2S sweeper of inorganic or organic metal salt in an amount effective to reduce the evolution of H2S . The H2S sweepers of inorganic or organic metal salt can be those described above. The description also includes roads made with these compositions that include aggregate.

A method is further provided to reduce the formation of pyrophoric iron pyrite in a storage vessel that involves in any order adding polymer modified asphalt to the container and adding a sweeping of H2S of inorganic or organic metal salt to the container in an amount effective to reduce the evolution of H2S from asphalt. Again, the metal of the H2S sweeper of inorganic or organic metal salt may be zinc, cadmium, mercury, copper, silver, nickel, platinum, iron and magnesium, including mixtures of these salts.

In an alternate, non-limiting embodiment of the description a method is provided for recycling asphalt that involves physically removing asphalt from a position and in any order reducing the size of the asphalt removed, heating the asphalt removed and adding a sweeper of H2S of metal salt. inorganic or organic asphalt in an effective amount to reduce the evolution of H2S. Again, the sweeper metal of H2S of inorganic or organic metal salt may be zinc, cadmium, mercury, copper, silver, nickel, platinum, iron and / or magnesium, including mixtures of these salts. The description also includes recycled asphalt made by this procedure, and polymeric elastomers can be added to these recycled asphalts.

The invention further involves an aggregate that includes an elastomer modified asphalt that covers at least partially the aggregate, where the elastomer modified asphalt comprises an inorganic or organic metal salt H2S sweeper in an amount effective to reduce the H2S evolution of the modified asphalt with elastomer. Again, suitable sweepers may be those described above.

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Detailed description of the invention

It has been found that significant reductions in H2S emissions during the production, storage and transfer of asphalt can be achieved by the addition of alkanolamines (such as ethanolamine), dimethalamine amines and / or inorganic metal salts.

As used herein, the term "bitumen" (sometimes referred to as "asphalt") refers to all types of bitumen, which include those that occur in nature and those obtained in the processing of oil. The choice of bitumen will essentially depend on the particular application envisaged for the resulting bitumen composition. The bitumen that can be used can have an initial viscosity of 60 ° C (140 ° F) of 60 to 300 Pa-s (600 to 3000 poise) depending on the degree of asphalt desired. The initial penetration range (ASTM D5 standard) of the bitumen at 25 ° C (77 ° F) is 20 to 320 dmm, and may alternatively be 50 to 150 dmm, when the intended use of the bitumen composition is the paved road. The amounts of asphalt typically employed by the methods of this invention will vary widely, but in a non-limiting embodiment of the invention, it may be at least about 2.27 kg (5 pounds) for roofing applications. In another case, it may be at least approximately 50,000 tons for paving applications.

The term "Desired Rheological Properties" refers primarily to the specification of SUPERPAVE asphalt binder designed by AASHTO as SP-1. Additional asphalt specifications may include viscosity at 60 ° C (140 ° F) of 160-400 Pa-s (1600 to 4000 poise) before aging; a hardness of at least 127 cm-kilogram (110 inch-pounds) before aging; a toughness of at least 86.6 cm-kilograms (75 inch-pounds) before aging; and a ductility of at least 25 cm at 4 ° C (39.2 ° F) at a discharge rate of 5 cm / min after aging.

Viscosity measurements are made using the ASTM D2171 test method. Ductility measurements are made using the ASTM D113 test method. The hardness and toughness measurements are made using a Benson Hardness and Tenacity Method, run at 50.8 cm / minute (20 inches / minute) of discharge velocity with a ball of 2.22 cm (1/8 inch) ) diameter.

By "stable storage viscosity" it is understood that the bitumen composition does not show evidence of peeling, settling, gel formation or granularity and that the viscosity of the composition does not increase by a factor of four or more during storage at 163 ± 2 , 8 ° C (325 ± 0.5 ° F) for seven days. In a non-limiting embodiment of the description, the viscosity does not increase by a factor of two or more during storage at 163 ° C (325 ° F) for seven days. In another non-limiting embodiment of the description, the viscosity increases less than 50% for seven days of storage at 163 ° C (325 ° F). A substantial increase in the viscosity of the bitumen composition during storage is undesirable due to the difficulties resulting in the handling of the composition and in the satisfaction of the product specifications at the time of sale and use.

The term "aggregate" refers to rock and similar material added to the bitumen composition to provide an aggregate composition suitable for paving roads. Typically, the aggregate used is natural rock from the area where the bitumen composition is produced. Suitable aggregate includes granite, basalt, limestone and the like.

As used herein, the term "asphalt cement" refers to any of a variety of substantially solid or semi-solid materials at room temperature that gradually liquefy when heated. Its predominant constituents are bitumen, which can occur naturally or be obtained as the refining process residue. The terms asphalt used herein are well known to those skilled in the art. For an explanation of these terms, reference is made to the brochure SUPERPAVE Series num. 1 (SP-1), printed in 1997, published by the Asphalt Institute (Research Park Drive, PO Box 14052, Lexington, KY 40512-4052), which is incorporated herein by reference in its entirety. For example, Chapter 2 provides an explanation of the test equipment, terms and purposes. The Rolling Fine Pellet Furnace (RTFO) and the Pressure Aging Vessel (PAV) are used to simulate the aging (hardening) characteristics of the binder. Dynamic Cut Reometers (DSR) are used to measure the properties of the binder at high and intermediate temperatures. This is used to predict permanent deformation or furrow formation and fatigue rupture. Flexion Beam Reometers (BBRs) are used to measure the properties of the binder at low temperatures. These values predict thermal breakage or low temperature. The procedures for these experiments are also described in the SUPERPAVE brochure referenced above.

The classification of asphalt is given in accordance with the standards accepted in the industry as discussed in the Asphalt Institute brochure referred to above. For example, pages 62-65 of the booklet include a table titled Performance Asphalt Binder Specifications. Asphalt compositions are given in degrees of performance, for example, PG 64-22. The first number, 64, represents the average temperature of the maximum pavement design of 7 days in ° C. The second number, -22, represents the minimum pavement design temperature in ° C. Other needs of each grade are shown in the table. For example, the maximum value for the PAV-DSR test, (° C) for PG 64-22 is 25 ° C.

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According to a non-limiting embodiment of the present description, an asphalt composition is prepared by adding the asphalt or bitumen to a mixing tank having stirring means. The asphalt is added and stirred at high temperatures. Stirring temperatures depend on the viscosity of the asphalt and can range up to 260 ° C (500 ° F). Asphalt products from refining operations are well known in the art. For example, asphalts typically used for this procedure are obtained from distillation to the deep crude oil ford to obtain a bottom product of the desired viscosity or from a solvent de-asphalting process that gives a demetallized oil, a resin fraction and a asphaltene fraction. Some refining units do not have a resin fraction. These materials or other compatible oils of more than 232 ° C (450 ° F) flash point can be mixed to obtain the asphalt of desired viscosity. In polymer modified asphalt (PMA) processing, care should be taken not to subject the asphalt / polymer composition to elevated temperatures for too long to avoid thermal degradation of the polymer.

As noted, it has been discovered that certain H2S sweepers have been found useful in preventing or inhibiting the evolution or emission of H2S from asphalt elastomer mixtures during processing. It will be appreciated that it is not necessary for the sweepers of H2S of this invention to completely eliminate the evolution or emission of H2S for the invention to be a success, since in some cases this may be impossible. The goal is to reduce at least the evolution of H2S to acceptable levels. In a non-limiting embodiment of the description, the acceptable level is the usual acceptable level to OSHA. In another non-limiting embodiment of the description, an acceptable level is 50 ppm or less, and in an alternative non-limiting embodiment of the description, an acceptable level is 10 ppm or less. It will also be noted that just because a compound has been previously identified as an H2S sweeper in a context does not mean that it will work well in the current method, as will be demonstrated. It has been found that alkanolamines and dimethalic amines are sweepers of H2S useful for road asphalt. Suitable alkanolamines include, but are not necessarily limited to, ethanolamine. Suitable dimethalamine amines include, but are not necessarily limited to, Dimethalic amine available from Betz Laboratories.

In the case where the H2S sweeper is an alkanolamine and / or a dimethalic amine, the sweeper can be added in an amount ranging from about 0.005 to about 2.0% by weight based on the mixture. In another non-limiting embodiment of the description, the amount may range from about 0.01 to about 1.0% by weight.

H2S sweepers of inorganic or organic metal salt have been found especially effective in reducing the evolution of H2S. The metal of the H2S metal salt sweeper can be zinc, cadmium, mercury, copper, silver, nickel, platinum, iron, magnesium and mixtures thereof. The organic and inorganic salt forms of these metals include, but are not necessarily limited to, carboxylates, oxides, nitrates, carbonates, hydrates, halides, phosphates, perchlorates, sulfates, sulphonates and the like and mixtures thereof. Specific examples of suitable organic metal salts include, but are not necessarily limited to, zinc stearate, calcium palmitate, magnesium citrate, and the like and mixtures thereof. In a non-limiting embodiment of the invention, the H2S sweeper of metal salt is zinc oxide, magnesium oxide and / or copper oxide. The zinc oxide species is often referred to herein as a non-limiting example, and is not intended to exclude other suitable H2S sweepers of metal salt.

It has also been particularly found that an excess of metal salt (for example, zinc oxide) than is normally used can inhibit the evolution or formation of H2S. Generally, in a non-limiting embodiment, the amount of H2S sweeper of inorganic or organic metal salt should be minimized sufficiently (up to about 3% by weight) to reduce hydrogen sulfide to desired levels. In a non-limiting embodiment of the invention, the H2S sweeper of inorganic or organic metal salt ranges from about 0.05 to about 2% by weight based on the mixture of asphalt and polymer. In another case, the amount of zinc oxide is at least 10 times that normally used.

In an alternative, non-limiting embodiment of the description, at least a part of, or optionally all of, a conventional sulfur-containing derivative (e.g., mercatobenzothiazole (MBT), thiuramas, dithiocarbamates, mercatobenzimidazole (MBI) and / or crosslinker of elemental sulfur for use on asphalts is replaced with a poly (alkyl sulfide) and / or a poly (ester sulphide) to reduce the emission of H2S from WFP during processing. The specific specific poly (alkyl sulfides) used in this invention include, but are not necessarily limited to TPS-32 poly (di-tert-dodecyl sulfide) from Atofina Chemicals Inc. Suitable poly (ester sulfides) used in this invention include, but are not necessarily limited to , VPS 17 sulfurized fatty ester available from Atofina Chemicals Inc. In another non-limiting embodiment of the description, the total amount of crosslinker and sulfide is present in an amount ranging from about 0.01 to approximately 0.6% by weight of active ingredients, based on the weight of the asphalt. In an alternative, non-limiting embodiment of the description, at least 50% by weight of the crosslinker that is added is usually replaced by a sulfide in this invention. At least partial replacement of the sulphide crosslinker may have the effect of reducing the amount of another scavenger of H2S used.

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In general, in a non-limiting embodiment of the invention, if the asphalt is modified with a polymer, it can emit more H2S if they are crosslinked.

The methods and compositions of this invention will be further illustrated with respect to particular Examples that are only intended to more fully illuminate the invention and not limit it in any way.

Examples 1-6

The need for the invention arose when H2S vapors in the 250-750 ppm range were detected emanating from a mixing tank where an asphalt / polymer mixture was mixing and grinding after the addition of cross-linking agent based on ZnO / MBT / S available from Atofina Petrochemicals, Inc. The crosslinking agent was mixed in an asphalt concentrate in the tank and pumped into a mixing / recessing tank for the crosslinking reaction and cure. There was no decrease in H2S in the asphalt / polymer mixing tank. Subsequent testing of the PMA storage tank and loading facility after zinc oxide treatment indicated that H2S levels were at or below a level of 10 ppm that is considered safe. Initially, Heat Loss (LOH) and smoke properties for several H2S sweepers were evaluated.

A mixture of 0.1% by weight of each of the H2S sweepers on an asphalt base was tested for smoke and LOH according to standard practices. The results are presented in Table I.

Table I

Results of the smoke and LOH test for asphalt / H2S sweeper formulations

 Example

 1 2 3 4 5 6

 Sweeping Product

 Amino Dimetalica Betz Unichem U-I- 7586 Betz Prosweet Baker Petrolite Enichem EC 5492A Enichem EC 9266A

 Kind

 Dimethyl amine KOH / amine Triazine Amine / aldehyde Amine Iron carboxylate

 LOH% at 1 peso

 0.1 0.1 0.1 0.1 0.1 0.1

 Smoke2

 0.066 0.077 0.254 0.0523 0.268 0.377

'% by weight loss versus net asphalt

2 "Smoke" - material caught in filters, in grams.

3The Baker Petrolite product began to smoke visibly immediately after the addition.

All asphalt / sweeper mixtures lost 0.1% by weight during RTFO aging. This is equivalent to the total amount of H2S sweeper added, although it should be understood that the weight loss may also have been due to some other asphalt component since a target is not marched. Thus, there was no difference between sweepers screened in LOH.

Ethanolamine Unichem U-1-7586 features wetting characteristics more similar to the Amina Dimetalica Betz product. Sweepers Betz Prosweet and Enichem EC 5492A and Enichem EC 9266 fear smoke generation properties 4 to 5 times than for Amina Dimetalica Betz or Unichem sweepers. Although the measured grams of smoke residue were low for the Baker Petrolite sample, this H2S sweeper seemed to have "evaporated" from the asphalt immediately after the addition with considerable visible smoke generation. It should be concluded that not all known H2S sweepers are suitable for use on asphalt. Unichem ethanolamine was selected to be tested in asphalt formulations for total H2S emissions.

Examples 7-15

Various variations in asphalt formulations for H2S emissions were tested in the laboratory. Variations included those in Table II:

Table II

Identity of examples 7-15 for the test of H2S emissions Example Composition - the previous numbers are in% by weight

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7 Base asphalt

8 Base asphalt with crosslinking agent based on 0.40 ZnO / MBT / S

9 Base asphalt with 0.06 ZnO / 0.06 MBT / 0.12 S

10 Base asphalt with 0.60 ZnO / 0.06 MBT / 0.12 S

11 Base asphalt with 0.06 of ZnO / 0.06 of MBT / 0.12 of S with 0.1% by weight of Betz Dimetamine Amine

12 Base asphalt with 0.06 ZnO / 0.06 MBT / 0.12 S with 0.1% by weight of Unichem Ethanolamine U-1-7585

13 Base asphalt with 0.06 ZnO / 0.06 MBT / 0.12 S at 138 ° C (280 ° F)

14 Base asphalt with 0.06 ZnO / 0.06 MBT / 0.71 VPS polysulphide 17. VPS polysulfide 17 is a

Sulfurized fatty ester available from Atofina Chemicals Inc.

15 Base asphalt with 0.06 ZnO / 0.10 DTDM - 4,4'-dithiodimorpholine Results

The results of the ratings for H2S for each of the nine formulations tested are presented in Table III. It should be noted that the presented concentrations of H2S are an accumulation of H2S trapped / collected during the duration of the experiment and are not a representation of the actual H2S present in the headspace gas at any given time. The ppm calculations are based on the starting weight of the asphalt and are used as relative comparisons of applied treatments.

The crosslinking agent concentration of ZnO / MBT / S based crosslinking agent (Example 8) was estimated as an active crosslinking agent distribution of 0.06 ZnO / 0.06 MBT / 0.12 active S, concentrations equivalents of active ingredient to a dry form normally used. The concentration of ZMBT / DTDM of Example 15 was taken from values previously used in another work. The concentration of VPS 17 in Example 14 was based on a 0.12% by weight distribution of total sulfur. The low temperature of 138 ° C (280 ° F) in Example 13 was selected because it is the lowest temperature at which the asphalt can be effectively pumped into many refineries.

It should be noted that the total H2S concentration presented was the cumulative amount removed from the steam. This was not representative of the emissions at any given point during the crosslinker addition stage, but was used as a relative measure of the total H2S emission potential for comparisons of the Examples with each other. The concentrations are expressed as ppm based on the weight of liquid asphalt (i.e., grams of H2S developed per 106 grams of asphalt). This is not equivalent to the concentration in the steam space.

Table III

Measured H2S emissions from selected asphalt formulations

 Units of Ex. 7 8 9 10 11 12 13 14 15

 Asphalt

 100% by weight * * * * * * * *

 ZnO / MBT / S

 Weight% 0.40

 Amina Betz

 % by weight 0.1

 Unichem

 Weight% 0.01

 ZnO

 % by weight 0.06 0.60 0.06 0.06 0.06 0.06

 MBT

 % by weight 0.06 0.06 0.06 0.06 0.06 0.06

 Sulfur

 % by weight 0.12 0.12 0.12 0.12 0.12

 ZMBT

 Weight% 0.05

 DTDM

 Weight% 0.10

 VPS-17

 Weight% 0.71

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 Units of Ex. 7 8 9 10 11 12 13 14 15

 Temperature

 ° F 350 350 350 350 350 350 280 350 350

 Temperature

 ° C 177 177 177 177 177 177 138 177 177

 H2S

 ppm <1 1701 519 <1 <1 <1 <1 <1 407

* The rest is asphalt

Base asphalt (Example 7) did not show measurable H2S, and was not considered a significant source of H2S emission under the conditions of this experiment. The head space in asphalt tanks is known to have high concentrations of hydrogen sulfide and should be tried to remove hydrogen sulfide before release to the environment. Example 8 with ZnO / MBT / S based crosslinker and Example 9 with addition of dry equivalent ZnO / MBT / S both had significant contributions to H2S emissions. It is not known why there is significantly more H2S emitted with this crosslinker than with the dry equivalent, when both crosslinking formulations have equivalent active ingredients (concentrations) of ZnO / MBT / S. It is possible that ZnO, which helps block sulfur and reduce H2S, does not dissolve / activate from the EVA granule (ethylene-vinyl acetate) of the crosslinker as fast as the solid suspension formulation of the dry equivalent. There was also a significant H2S emitted during crosslinking with ZMBt / DTDM in Example 15.

It was found that treatment with ten times the normal amount of ZnO (Example 10), or the H2S Sweeper Amina Dimetalica Betz (Example 11) or the Unichem ethanolamine U-1-7585 (Example 12) eliminates the measurable emissions of H2S in This experiment However, when the asphalt is heated while it is being loaded into the truck, hydrogen sulfide is released from the amine salt / hydrogen sulfide. The reduction in crosslinker addition / mixing temperature at 138 ° C (280 ° F) also eliminated measurable H2S. However, there are time limitations in reducing asphalt operationally: the temperature below normal storage temperatures, although some temperature reduction may be considered.

The use of VPS-17 polysulfide (sulfur content equivalent to 0.12% by weight) led to the total emission of H2S at near tolerance levels. The measured concentration of 81 ppm of H2S was collected over a period of 3 hours and is most likely below the limit of 50 ppm at any given time during the addition of crosslinker. Certainly the H2S level could be minimized at any time by controlling the rate of polysulfide addition.

Examples 16-20

Zinc oxide has been shown to be effective in the treatment of asphalt for H2S. It was surprisingly discovered that CaO does not reduce H2S to levels measured after treatment with ZnO. An asphalt of the vacuum tower bottoms (VTB) was also treated with MgO or CuO and tested for H2S emissions. The results are shown in Table IV. The H2S measurements (in ppm) are representative of the total H2S collected during the experiment and are calculated based on the total asphalt weight. The results are not representative of the vapor space concentration at any given time.

Table IV

Results of the H2S assessment for DEMEX load treated with ZnO and CaO.

 H2S units

 VTB asphalt load

 ppm * 28

 Asphalt load of VTB + 0.1% ZnO

 ppm * <1

 Asphalt load of VTB + 0.1% CaO

 ppm * 36

 Asphalt load of VTB + 0.1% MgO

 ppm * <1

 Asphalt load of VTB + 0.1% CuO

 ppm * <1

The asphalt sample treated with ZnO subjects H2S levels below the 1 ppm detection limits of the assay. Treatment of the asphalt sample with both MgO and CuO resulted in H2S levels collected below the 1 ppm detection limit of the titration method used for this test. The asphalt sample treated with 0.1% by weight of CaO subject H2S measurable at 36 ppm, above the measured H2S of the untreated asphalt sample at 28 ppm.

Calcium has the lowest electronegativity of the metals used in this experiment. It is known that CaS breaks down into even weak acids, the release of H2S-ZnS is significantly more stable. The CaO is not

a viable option for the substitution of ZnO for the treatment of H2S in base asphalt reserves. MgO and CuO seem to offer the same or similar levels of H2S reduction as ZnO on asphalt. Thus, the treatment of asphalt with 0.1% by weight of CaO does not result in a decrease in the emission of H2S; the treatment of asphalt with 0.1% by weight of ZnO, 0.1% by weight of MgO, or 0.1% by weight of CuO decreases the 5 H2S emissions below the detection limit of the 1 ppm rating .

In the foregoing report, the invention has been described with reference to specific embodiments thereof, and has been shown to be effective in providing methods for preparing asphalt and polymer asphalt compositions with emissions or reduced evolution of H2S. However, it will be apparent that various modifications and changes can be made to the method without departing from the broader spirit or scope of the invention as presented in the 10 claims added. Therefore, memory will be considered in a more illustrative than restrictive sense. For example, combinations or specific amounts of asphalt, polymer, H2S sweepers of inorganic or organic metal salt and other components that fall within the claimed parameters, but not specifically identified or attempted in a particular asphalt system, are anticipated and expected. that are within the scope of this invention. Specifically, it is expected that the method and discovery of the invention 15 will work with H2S sweepers other than those exemplified herein.

The H2S sweepers of this invention can also be used to reduce the evolution of H2S in asphalts used to build roads, seal roofs, and other applications. They can also work to reduce the formation of pyrophoric iron pyrite in containers and tanks where asphalt is stored. Recycled asphalts can also treat you with these sweepers, and aggregates coated at least partially with asphalts 20 can be advantageously treated with these sweepers.

Claims (14)

5 10 fifteen twenty 25 30 35 40 Four. Five fifty 1. The method of preparing a polymer modified asphalt having reduced emissions of hydrogen sulfide, which comprises to. heating a mixture of asphalt and a conjugated diene vinyl / elastomeric aromatic polymer; b. add a crosslinker to the mixture where the crosslinker is elemental sulfur; Y, C. add a sweeper of H2S of inorganic or organic metal salt to the asphalt modified with the polymer in an amount ranging from 0.05 to 3% by weight based on the mixture of asphalt and polymer, where the metal of the H2S sweeper of salt Metallic is selected from the group consisting of zinc, cadmium, mercury, copper, silver, nickel, platinum, iron, magnesium and mixtures thereof. 2. The method according to claim 1, characterized in that the metal of the H2S sweeper of metal salt is selected from the group consisting of zinc, cadmium, copper, magnesium and mixtures thereof. 3. The method according to claim 1, characterized in that the inorganic or organic metal salt is selected from the group consisting of zinc oxide, cadmium oxide, copper oxide, magnesium oxide and mixtures thereof. 4. The method according to claim 1, characterized in that the H2S sweeper of inorganic or organic metal salt is selected from the group consisting of carboxylates, oxides and mixtures thereof. 5. The method according to claim 1, characterized in that the crosslinker is present in an amount ranging from 0.01 to 0.6% by weight of active ingredients, based on the weight of the asphalt / polymer mixture. 6. The method according to claim 1, characterized in that the amount of asphalt is at least 2.27 kg [5 pounds]. 7. Polymer modified asphalt, with reduced emissions of hydrogen sulfide, characterized in that the polymer modified asphalt comprises an H2S sweeper of inorganic or organic metal salt in an amount ranging from 0.05 to 3% by weight in base to the mixture of asphalt and polymer, where the metal of the H2S sweeper of inorganic or organic metal salt is selected from the group consisting of zinc, cadmium, mercury, copper, silver, nickel, platinum, iron, magnesium and mixtures of themselves, and where the crosslinker consists of elemental sulfur. 8. The polymer modified asphalt according to claim 7, wherein said polymer modified asphalt is recycled. 9. The aggregate composition comprising a polymer modified asphalt as defined according to claim 8, wherein the polymer is an elastomer, and an aggregate, wherein the aggregate is at least partially coated by the polymer modified asphalt. 10. The use of polymer modified asphalt as defined in claim 8 to construct roads or to seal a roof. 11. The use according to claim 10, which consists of sealing a roof with the polymer modified asphalt comprising heating the polymer modified asphalt and distributing it over at least a part of a roof surface. 12. The use according to claim 10, which consists in the construction of a road comprising combining the modified asphalt with polymer with aggregate to form a road paving material, and using the material to form road pavement. 13. The use of an H2S sweeper of inorganic or organic metal salt, where the H2S sweeper metal of inorganic or organic metal salt is selected from the group consisting of zinc, cadmium, mercury, copper, silver, nickel, platinum, iron, magnesium and mixtures thereof, to reduce hydrogen sulfide emissions from a polymer modified asphalt, where the H2S sweeper of inorganic or organic metal salt is added to the polymer modified asphalt in an amount ranging from 0 , 05 to 3% by weight based on the mixture of asphalt and polymer, and where the crosslinker consists of elemental sulfur. 14. The use of an H2S sweeper of inorganic or organic metal salt, where the H2S sweeper metal of inorganic or organic metal salt is selected from the group consisting of zinc, cadmium, mercury, copper, silver, nickel, platinum, iron, magnesium and mixtures thereof, to reduce the formation of pyrophoric iron pyrite in a storage vessel containing a polymer modified asphalt, where the H2S sweeper of inorganic or organic metal salt is added to the polymer modified asphalt in an amount ranging from 0.05 to 3% by weight based on the mixture of asphalt and polymer and where the crosslinker consists of elemental sulfur.